What kind of incentive effect a particular tax credit will have is certainly important, given the objective. In the context of a tax credit, as Pierre said earlier, you have to look at the factors that might influence somebody to take up a particular activity and where financial incentives fit within those factors. In addition, with the tax system, you're looking at people filing their taxes in the winter or the spring, so there may be a delay between when they undertake the activity and when they actually receive that financial incentive.
When you're looking at that cost, I think another important factor is the extent to which you're providing an incentive to people who were already going to undertake that activity to begin with. If you look at the full cost of the measure and then divide that over the incremental users, what is that per-user cost and how does that compare to other ways of addressing an objective?